Sunday, October 9, 2011

Medial Malleolar Fractures: A Biomechanical Study of Fixation Techniques

Medial Malleolar Fractures: A Biomechanical Study of Fixation Techniques
by T. Ty Fowler, MD; Kevin J. Pugh, MD; Alan S. Litsky, MD, ScD; Benjamin C. Taylor, MD; Bruce G. French, MD
DOI: 10.3928/01477447-20110627-09

Abstract

Fracture fixation of the medial malleolus in rotationally unstable ankle fractures typically results in healing with current fixation methods. However, when failure occurs, pullout of the screws from tension, compression, and rotational forces is predictable. We sought to biomechanically test a relatively new technique of bicortical screw fixation for medial malleoli fractures. Also, the AO group recommends tension-band fixation of small avulsion type fractures of the medial malleolus that are unacceptable for screw fixation. A well-documented complication of this technique is prominent symptomatic implants and secondary surgery for implant removal. Replacing stainless steel 18-gauge wire with FiberWire suture could theoretically decrease symptomatic implants. Therefore, a second goal was to biomechanically compare these 2 tension-band constructs.
Using a tibial Sawbones model, 2 bicortical screws were compared with 2 unicortical cancellous screws on a servohydraulic test frame in offset axial, transverse, and tension loading. Second, tension-band fixation using stainless steel wire was compared with FiberWire under tensile loads. Bicortical screw fixation was statistically the stiffest construct under tension loading conditions compared to unicortical screw fixation and tension-band techniques with FiberWire or stainless steel wire. In fact, unicortical screw fixation had only 10% of the stiffness as demonstrated in the bicortical technique. In a direct comparison, tension-band fixation using stainless steel wire was statistically stiffer than the FiberWire construct.
For unstable ankle fractures that involve the medial malleolus, operative treatment is generally recommended. 1–7 Multiple techniques, including bioabsorbable implants, 8 have been used for fixation of the medial malleolus; however, the most common technique as recommended by the Association for the Study of Internal Fixation (AO-ASIF) group uses two 4-mm partially threaded cancellous lag screws placed perpendicular to the fracture line. Stainless steel cancellous screws had up to 24% less pullout force, significantly less torsional and bending strength than a 3.5-mm bicortical screw.
The AO-ASIF group recommends tension-band wiring for small avulsion type fractures of the medial malleolus that are unacceptable for screw fixation as well as for osteoporotic bone. 5 A well-documented complication of tension-band fixation of the medial malleolus is prominent symptomatic hardware, largely due to the subcutaneous nature of the medial malleolus, that often requires a second operation for hardware removal. 2–4,12,13 Replacing stainless steel wire with Fiber-Wire (Arthrex Inc, Naples, Florida) suture could theoretically decrease the incidence of symptomatic hardware and therefore decrease secondary procedures.
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